In this courtroom sketch, David Coleman Headley appears before US District Judge Harry Leinenweber at federal court in Chicago, Thursday, as Leinenweber imposes a sentence of 35 years in prison for the key role Headley played in a 2008 terrorist attack on Mumbai that has been called India's 9/11.

Tom Gianni/AP

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A federal judge in Chicago sentenced an American citizen to 35 years in prison on Thursday for his role in providing surveillance information and videos laying the groundwork for the 2008 terror attacks in Mumbai, India, that left more than 160 dead and hundreds wounded.

David Coleman Headley, a US citizen of Pakistani heritage, was arrested in October 2009. He agreed shortly afterward to cooperate with US investigators and intelligence officials, and he testified against one of his fellow co-conspirators.

Among other information, Mr. Headley told US officials of a link between the terror operation in India and Pakistan’s intelligence service, the ISI. He identified his ISI contact as “Major Iqbal,” according to court documents.

In light of his cooperation, prosecutors did not seek the death penalty for Headley. In addition, instead of a life sentence, prosecutors urged US District Judge Harry Leinenweber to impose a 30 to 35-year prison term.

During the sentencing hearing, Judge Leinenweber called Headley a “terrorist” and rejected suggestions he had reformed his life.

“I don’t have any faith in Mr. Headley when he says he’s a changed person and believes in the American way of life,” the judge said, according to the Associated Press.

In their sentencing memorandum, prosecutors acknowledged that Headley played “an essential role in the planning of a horrific terrorist attack.”

“There is little question that life imprisonment would be an appropriate punishment for Headley’s incredibly serious crimes,” they said. But they added that his extensive cooperation had been of “significant value” to US anti-terror efforts.

Headley, 52, is unlikely to emerge from prison until he is well into his 80s.

Headley pleaded guilty in March 2010 to all 12 counts in his indictment. The charges included conspiracy to bomb public places in India, conspiracy to murder and maim persons in India, and six counts of aiding and abetting the murder of US citizens in India.

Among the dead were six American citizens.

Headley attended a series of training camps in Pakistan in 2002 and 2003. He later decided to change his name from Daood Gilani to David Headley to allow him to conceal his Pakistani ties and portray himself as an American in India.

Headley told investigators that he made five trips to Mumbai in 2006, 2007, and 2008 to survey and videotape potential targets for a planned assault team from the Pakistani terror group Lashkar-e-Taiba.

At one point he used a GPS device to pinpoint potential landing spots for the assault team along the shores of Mumbai harbor.

The attacks were carried out from Nov. 26 to Nov. 28, 2009 by 10 men trained by Lashkar-e-Taiba. They were armed with assault rifles, grenades, and improvised explosive devices, and they killed indiscriminately.

Targets included the Taj Mahal Hotel, Oberoi Hotel, the Leopold Café, a Jewish center called the Chabad House, and the train station. Headley had provided surveillance of each of those targets.

Four months after the attacks, Headley returned to India to conduct surveillance of India’s National Defense College in Delhi and Chabad Houses in several other cities, officials said.

Headley was also asked to provide surveillance in advance of planned attacks on the Danish newspaper Morgenavisen Jyllands-Posten, which had published a controversial cartoon depicting the Prophet Mohammed in a derogatory light. The action prompted calls from Islamic militants – including members of Al Qaeda – for retaliation.

Headley traveled to Denmark in January 2009 and produced videos that he turned over to a Lashkar member later that month during a trip to Pakistan. He returned to Europe in July and August 2009 and produced 13 additional surveillance videos in Denmark.

Headley was arrested at Chicago’s O’Hare International Airport in Oct. 2009 while preparing to board a flight to Pakistan to deliver the 13 videos.

As part of his cooperation he testified at the June 2011 trial of alleged co-conspirator Tahawwur Rana of Chicago. Mr. Rana was convicted of providing material support to the Denmark plot and providing material support to Lashkar.